| Frequency inverter Overheat | Radiator temperature ≥ oh Detection Value (about 80°C, from temperature switch) |
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ERR15 – Frequency Inverter Overheat
What this means
ERR15 indicates that the VFD has overheated.
Specifically, the internal temperature sensor has detected the heatsink (radiator) temperature reaching or exceeding the protection threshold, typically around 80°C (176°F).
To prevent permanent damage, the VFD shuts itself down.
Why This Happens
VFDs generate heat during normal operation, especially under load.
They rely on:
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Internal cooling fans
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Adequate airflow
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Reasonable ambient temperatures
If heat cannot be removed fast enough, the VFD will fault.
Most Common Causes We See
1. Restricted airflow (most common)
Examples:
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VFD installed in a sealed or undersized enclosure
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Air vents blocked or covered
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No active ventilation in an enclosure
Even a correctly sized VFD will overheat if it cannot breathe.
2. Cooling fan not operating
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Fan failed
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Fan obstructed by debris
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Fan wiring disconnected
A non-functioning fan will cause rapid temperature rise under load.
3. High ambient temperature
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Shop temperature too high
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Enclosure mounted near heat sources
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Direct sunlight on enclosure
VFD cooling assumes reasonable ambient conditions.
4. Dirt and dust buildup
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Dust clogging air intakes
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Debris coating the heatsink fins
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Restricted airflow paths
This is common in woodworking environments over time.
5. Sustained heavy load
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Running near maximum current for extended periods
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Aggressive cutting without cooldown periods
This generates more heat than light or intermittent use.
6. Faulty temperature sensor (rare)
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Thermistor or temperature switch failure
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Internal sensor wiring issue
This is uncommon and typically only considered after airflow issues are ruled out.
What to Check First
Step 1: Verify fan operation
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Power on the VFD
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Confirm the cooling fan spins freely
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Listen for abnormal fan noise
If the fan is not running, stop operation immediately.
Step 2: Check airflow and enclosure design
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Ensure vents are unobstructed
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Confirm enclosure allows airflow in and out
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Add ventilation fans if the enclosure is sealed
A VFD enclosure must be ventilated.
Step 3: Inspect for dust buildup
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Power down and unplug the VFD
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Clean exterior vents and intake areas
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Remove dust from heatsink fins if accessible
Regular cleaning is important in CNC environments.
Step 4: Evaluate ambient temperature
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Measure shop temperature
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Avoid mounting near other heat sources
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Improve airflow around the enclosure
Step 5: Reduce sustained load (if applicable)
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Reduce cutting aggressiveness
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Allow cooldown periods during long jobs
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Verify spindle and VFD are appropriately sized for the work
What ERR15 Is Not
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Not a wiring fault
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Not a controller or software issue
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Not EMI related
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Not a spindle motor fault
ERR15 is strictly a thermal protection fault.
How to Clear ERR15
Once the VFD cools down:
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Restore proper airflow
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Reset the VFD
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Resume operation
If ERR15 returns quickly, airflow or cooling must be addressed before continuing.
Summary
ERR15 means the VFD has overheated and shut down to protect itself.
Most common causes:
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Poor ventilation
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Failed or obstructed cooling fan
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High ambient temperature
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Dust buildup
Ensure proper airflow and cooling before resuming operation.
